(1) Field of the Invention
The present invention relates generally to cutting systems for cutting a garment pattern from a tubular knit fabric lay and, more particularly, to a centerline detector for a tubular knit fabric lay cutter.
(2) Description of the Prior Art
Fabric cutting is typically performed on a multiplicity of fabric layers referred to as fabric plies. The multiplicity of fabric plies are vertically arranged to form a fabric lay which is moved into a cutting assembly for cutting the plies simultaneously according to a predetermined arrangement of fabric sections which may have varying size and shape.
Generally, the vertical arrangement of fabric plies produces a fabric lay with nonuniform edge alignment which results in fabric waste or nonuniform cut fabric sections. More particularly, for tubular knit fabric lays, the amount of edge waste and/or the number and probability of non-uniform cut fabric sections involving the folded edges is substantially increased.
Various prior art fabric cutting systems have attempted to measure and control the fabric longitudinal centerline with respect to the cutter in order to decrease the amount of edge waste due to nonuniform edge alignment within the fabric lays. Although the prior art has sought to decrease fabric waste due to section cut layout inefficiency via automated cutting systems which optimize section layout within a given fabric length, such prior art systems have relied upon manual measurement of the fabric edges and calculation of the fabric lay centerline therefrom, generally by interpolation between two points measured at predetermined fabric intervals. Fabric cutting patterns were then readjusted based upon those centerline values.
Fabric lay centerline points determined from prior art manual measurements of the nonuniform edges have typically produced centerline error in the range of +/-6 mm within a given fabric length. Particularly for tubular knit fabric lays where fabric sections are cut around the folded edges, fabric lay centerline measurement error is substantially increased because the amount of waste is magnified by at least a power of two for the edge cut sections. When, rarely, cuts are made with respect to both folds, the effect of the error increases to four times! Thus, 5 mm error on both folds of a matching front and back garment piece could result in a 20 mm error in the seam location. This error would be sufficient to produce a second quality, low profit garment.
One prior art alternative to centerline calculation involved fabric lay alignment along one edge of the fabric lay. While this method reduces the need for highly accurate centerline measurements, a substantial amount of waste is still produced along the nonaligned edge. For tubular knitted fabrics, further waste results because fabric section cutting may not be optimized without use of both folded edges.
Thus, there remains a need for a fabric lay centerline detector for automatically measuring and determining the centerline of a fabric lay, particularly for tubular knit fabric lays, whereby the centerline determination error is substantially reduced thereby decreasing fabric waste and folded edge cut section non-uniformity while, at the same time, can make an accurate measurement even when the fabric lay is covered by a plastic vacuum film.